Method for controlling an orthopedic joint

ABSTRACT

A method for controlling an orthopedic joint of a lower extremity in at least one degree of freedom by means of an adjustable actuator for adjusting an orthopedic apparatus to walking situations that differ from walking on a plane. The orthopedic apparatus comprises top connecting members to connect to a limb, and an orthopedic element that is hingedly arranged distal to the connecting members. The method includes sensing, with sensors, several parameters of the orthopedic apparatus; comparing the sensed parameters with criteria that have been established based on several parameters and/or parameter curves and are stored in a computer unit; selecting a criterion that is suitable on the basis of the determined parameters and/or parameter curves; and adjusting resistances to movements, extents of movements, driving forces, and/or the progresses thereof in accordance with the selected criterion in order to control special functions that differ from walking on a plane.

The invention relates to a method for controlling an orthopedic joint ofa lower extremity in the flexion and/or extension direction by means ofan adjustable actuator for adapting an orthopedic appliance to walkingsituations that deviate from walking on the plane. The orthopedicappliance comprises upper means of attachment to a limb, and anorthopedic element arranged in an articulated manner distally of theattachment means.

DE 10 2006 021 802, as a later published document, relates to thecontrol of a passive prosthetic knee joint with adjustable damping inthe direction of flexion such that a prosthetic appliance, with upperattachment means and with a connection element to an artificial foot,which is secured on the prosthetic knee joint, can be adapted forclimbing stairs. The low-torque lift of the prosthetic foot is detected,and the flexion damping in the lift phase is then reduced to below alevel that is suitable for walking on a plane.

Proceeding from this prior art, the object of the invention is to makeavailable a method for controlling an orthopedic joint, with whichmethod it is possible to take account of particular walking situationsand to ensure a suitable behavior of the orthopedic appliance.

According to the invention, this object is achieved by a method havingthe features of the main claim. Advantageous embodiments anddevelopments of the method are set forth in the dependent claims.

In the method according to the invention for controlling an orthopedicjoint, which is understood to include prosthetic joints and alsoorthotic joints of a lower extremity, in at least one degree of freedom,an adjustable actuator is used to permit adaptation to different walkingsituations, for example by changing the damping in the flexion and/orextension direction.

The orthopedic appliance in which the orthopedic joint is integrated canbe an orthosis or prosthesis, for example a prosthetic knee joint withdistal attachment means for a prosthetic foot and with proximalattachment means to a limb. Provision is also made for the orthopedicappliance to comprise only a prosthetic foot joint with an artificialfoot secured thereon and with attachment means to a below-knee stump. Inaddition to the exoprostheses, knee or ankle joint orthoses are alsoprovided that can be controlled using the method. In the case oforthopedic knee joints, the orthopedic element arranged in anarticulated manner distally of the attachment means is formed, inorthoses, by the below-knee rails with the foot holder, and, inprostheses, by the below-knee shaft with the prosthetic foot. In thecase of orthopedic appliances for the ankle joint, a foot holder andmeans for securing on the lower leg are to be provided for orthoses, anda prosthetic foot with means of attachment to a lower leg are to beprovided in prostheses.

Sensors are arranged on the orthopedic appliance and detect severalparameters of the orthopedic appliance or of the limb. These detectedparameters are compared with criteria that have been established on thebasis of several parameters and/or parameter profiles. On the basis ofthese criteria, which are stored in a computer unit and which assignspecific movement states or load states of the orthopedic appliance tospecific walking situations, a specific criterion is selected that isregarded as the most suitable on the basis of the detected parametersand/or parameter profiles. It is possible in principle that severalcriteria also have to be regarded as suitable on the basis of thedetermined parameters or parameter profiles. Then, either a selection ismade on the basis of additional criteria, or several special functionsare superposed. The sensors determine the parameters during walking,preferably during walking on a plane, such that the user of theorthopedic appliance has the possibility of initiating the specialfunctions without having to perform movements that are not consistentwith the natural pattern. By virtue of slight deviations of individualparameters being detected during walking and being evaluated incorrelation with other parameters and deviations, which have beencombined to form criteria, it is possible for forthcoming movementsequences to be estimated, such that the special function can beinitiated from walking. While it is known from the prior art to activatespecial functions through unusual movement sequences when standing, e.g.through repeated and rapid loading of the front foot or through anundulating movement resulting from atypical alternate loading of theheel and front foot, it is possible, with the method according to theinvention, to effect a change-over from walking, which results in an“intuitive” control that does not require any deliberate maneuvers. Thisincreases the wearing comfort and improves safety, particularly forprosthesis wearers, since incorrect operation is minimized or excluded.

In order to control special functions that deviate from walking on aplane, provision is made that movement resistances, movement ranges,drive forces and/or the profiles thereof are adapted in accordance withthe selected criterion. The special function is controlled or initiatedon the basis of the selected criterion or of the selected criteria, andthis comprises, for example, the flexion damping and/or extensiondamping being adapted to a level that deviates from the level suitablefor walking on a plane, a catch being released, a drive being adjustedand/or a limit stop being adjusted. By changing the setting of thepassive components such as hydraulics, brakes or limit stops, noadditional kinetic energy is supplied to the orthopedic appliance, suchthat it is also possible in this context to talk of passive actuators.Adjustment of the passive actuators, e.g. reduction of a cross sectionof flow by moving a slide, also requires energy, but this does notresult in an increase of the kinetic energy of the prosthesis ororthosis. Active actuators are understood as pumps, electric drives orthe like, which can actively assist the movement sequence. The actuatorsused can be switches, pumps, electric motors, energy stores or otherdrives. The energy stores are provided in the form of, for example,springs, pressure accumulators or the like, from which the energy storedtherein can be released in a controlled manner to an appliance.

In this way, it is possible to perform special functions, e.g.alternating climbing of stairs, with a prosthetic knee joint, and tomake climbing stairs easier for a prosthesis wearer, without the dangerof the prosthetic leg suddenly buckling or being left suspended below astep. It is thus also possible to be able to call up the specialfunctions from different starting positions, for example when walking upstairs is to be performed from standing, with the prosthetic side firstor with the contralateral side first, when the first step is to be takenor when the last step is reached. It is likewise possible to call up thespecial function from a starting position via several differentcriteria, if several criteria significantly indicate a specific,expected walking pattern or an expected walking situation. This as awhole permits an automatic control of the joint, without the user of theorthopedic appliance deliberately having to perform a maneuver thatdeviates from a natural movement sequence.

It is thus possible for the prosthesis/orthosis wearer to be providedwith an orthopedic appliance that adapts to the particular situation,without the need for a long period of accustomization to the extendedfunction. The invention exploits the fact that the relevant startingpositions and walking situations have a specific, significant loading orloading sequence or parameter sequence, which are suitable forestablishing criteria for calling up special functions and forcorrespondingly changing the degrees of freedom, in particular thedamping, such as the flexion damping and/or extension damping.

In particular, a control of a passive joint is possible with theadjustment of the damping, and provision is likewise made that a catch,for example a limit stop catch, is released or set, or a limit stop isadjusted, such that a variable flexion angle can be realized. Inaddition, it is possible for a drive to be adjusted, such that specificelements of the orthopedic appliance are actively adjusted, for examplea support of the extension movement or of a flexion movement in the footor in the knee joint.

As a parameter of the criteria that are used to trigger one or morespecial functions, it is possible to use the axial force or the profileof the axial force in the components of the orthopedic appliance, forexample in the below-knee rail of an orthosis or in the below-knee shaftof a knee prosthesis. The force profile used in this case is an increaseor a decrease in an axial force, the change in the profile of an axialforce, and the speed of a decrease in an axial force. In order todetermine these parameters, force sensors are used which determine theaxial force within the orthopedic appliance. By repeated measurement,preferably in short cycles, the profile of the axial force can then bedetermined.

Provision is also made that the parameter used and taken into account inthe selection of special functions is the joint angle or the profile ofa change in the joint angle. The change in the joint angle is determinedin the form of a pivoting speed or of an acceleration about the jointaxis during walking. The joint angle can be used, for example, todetermine the relative position of the components of the orthopedicappliance, and this makes it possible to detect specific phases ofwalking and to draw conclusions from this regarding the walkingsituation that is to be expected and/or to determine or estimate theload that is to be expected on the orthopedic appliance.

Moreover, the torque acting in the joint, a change in the joint torqueor a profile of a change in the joint torque can be used as parameters,since every walking situation can at a specific point in time beassigned a specific torque value. From the joint torque in one phaseitself, or from the profile of the change in the joint torque, it ispossible to determine whether and in which walking situation the user ofthe orthopedic appliance is located and which additional dampingadjustments have to be performed in order to support the next walkingsituation in the best possible manner.

Provision is further made that a vertical movement of at least onecomponent of the orthopedic appliance is detected and is used as aparameter for determining the initiation of a special function, whenthis parameter, together with other parameters, lies within a specificvalue range and thus satisfies fixed criteria. In addition to a purelyvertical movement, which is likewise detected via corresponding sensors,a profile of a vertical movement can also be used as parameter, that isto say the speed of a vertical movement or a vertical acceleration, inorder to determine in which starting position the patient is located andwhich walking situation is to be expected.

Surprisingly, it has been found that a horizontal movement and/or aprofile of a horizontal movement can also be used as parameter. Whenclimbing stairs using an orthopedic appliance, it has been shown that,during walking, a lower leg that is guided rearward, i.e. counter to thedirection of walking, supplies reliable signals. The knee is in thiscase positioned clearly in front of the ankle joint in the direction ofwalking.

It is likewise useful, for control of the orthopedic appliance, if atilt angle of part of the orthopedic appliance in space is determined,that is to say the inclination that a component has in space. This caneither be measured via an absolute angle sensor, which has a spatialorientation as reference variable, for example the direction ofgravitational force, or can be computed from various other sensor data.In addition to the instantaneous tilt angle, it is likewise possible fora change in the tilt angle and the profile of the change in the tiltangle of part of the orthopedic appliance to be used as a parameter inorder to decide which special functions are initiated, and when they areinitiated, in the damping of the orthopedic appliance. The tilt anglecan be determined from the acceleration and angular velocity that wererecorded by acceleration sensors and a gyroscope.

Preferably, several parameters or parameter profiles are combined in onecriterion, that is to say two or more parameters, in order to determinethe starting state as accurately as possible on the basis of the sensordata and to reach a precise association and decision as to which specialfunction is initiated.

Provision is likewise made that several criteria or the meeting ofseveral criteria can initiate a special function. This takes account ofthe fact that a special function, for example the alternating climbingof stairs, is started from different walking speeds, differentpositions, or with the prosthetic leg first or the healthy leg first. Itcan therefore happen that precisely one special function has to beinitiated, but different criteria can be satisfied in order to ensurethat precisely this special function is initiated.

In a development of the invention, the control method, in the specialfunction, increases the extension damping and/or flexion damping in aset-down and hip-straightening phase of the lower extremity to a levelabove a damping of a swing phase control for walking on a plane. In thisway, it is possible to effect a controlled extension or straighteningboth of the hip joint and also of the knee joint and ankle joint.

To climb over an obstacle, it is necessary that, in the lift phase, theflexion damping is first reduced and then the extension damping, so asto ensure that the greatest possible step can be taken, since anobstacle has to be overcome, for example the threshold of a door or anobject lying on the ground, and the foot or prosthetic foot is notintended to be set down on a next higher step. After the foot has beenset down, however, provision is made that, in the special function, theflexion damping and/or extension damping in the set-down phase isincreased to a maximum value, this applies both to alternating climbingof stairs and also to overcoming obstacles, such that the knee joint,when straightening, is secured against buckling or against hard contactwith the end stop. Provision is likewise made that, directly before thefoot or prosthetic foot is set down, the extension damping is increasedbefore the straightening, such that the positioning of the foot orprosthetic foot can be effected by the hip angle that is directlycontrollable by the patient. Increasing the flexion damping to a maximumvalue has the advantage that, if the hip-straightening moment isinadequate, giving-way of the knee is reduced or avoided. The highdegree of damping in the set-down and hip-straightening phase is in thiscase preferably maintained until straightening of the hip is complete.

The original flexion damping within the joint can preferably beincreased in accordance with the change in the knee angle, since a greatdeal of information concerning the starting state can be determined fromthe knee angle. As soon as a fixed knee angle is reached that isgenerally greater than a knee angle suitable in swing phase control forwalking on a plane, the flexion damping is increased. Alternatively orin addition, the flexion damping can be increased or decreased inaccordance with the axial force acting on the below-knee shaft or on thebelow-knee component. If the axial force drops sufficiently quickly toapproximately 0 with the knee almost straight, this is an indicator forinitiation of a stair-climbing mode, such that a specific control can beeffected within the damper devices.

Provision is alternatively made that, in the case of an orthopedic kneejoint, the special function is initiated when an axial force acting onthe below-knee shaft drops to a specific value and when the knee jointis straightened or being straightened, and the flexion damping isreduced in the special function. The absolute value of the axial forcecan be used as an additional parameter in order to define a criterion.If the axial force drops below a fixed level, the special function isinitiated, and the flexion damping is then reduced in the specialfunction.

In addition or alternatively, provision is made that, in the case of anorthopedic knee joint, the special function is initiated when the lowerleg is inclined rearward, the knee joint is straightened and a kneetorque is below a fixed level, and, in the special function, the flexiondamping is reduced to below a fixed value. A rearwardly inclined lowerleg is present when the knee joint is located clearly in front of theankle joint.

Provision is likewise made for the special function to be initiated whenthere is an upward vertical acceleration and when an axial force isbelow a fixed level, which special function effects a change in theflexion damping and/or extension damping, and for the flexion damping tobe reduced in the special function.

In one variant, the special function is initiated when there is arearward horizontal acceleration, that is to say counter to thedirection of walking, and when an axial force is below a fixed level,and the flexion damping is reduced in the special function.

The flexion damping and/or extension damping is adjusted preferablyduring the lift phase and/or set-down phase, for example when the footor the prosthetic foot is set down again after being lifted and anincrease in the axial force is then determined. Likewise, with a kneeangle remaining approximately constant, the extension damping andflexion damping can be increased, since this is associated with a lowmechanical resistance and can therefore be performed with relativelylittle energy. The flexion damping can be reduced in the lift phase to aminimum value, such that the damping effective in every system onaccount of friction is not further increased.

Alternatively, provision is made that the damping is adjusted during thestance phase or swing phase.

It is likewise possible that a low-torque lift of the distally arrangedorthopedic element is detected via a force sensor or torque sensor, saiddetection being able to take place mechanically, likewise the change inthe various dampings, in order to obtain the simplest possible structureof the orthopedic appliance that is to be controlled. After thelow-torque lift of the distal orthopedic element has been detected, theflexion damping can likewise be reduced, specifically to a level that isbelow a level suitable or optimized for walking on a plane.

By means of the reduction in the flexion resistance, by reducing theflexion damping, it is possible to obtain a joint angle that allows aprosthetic foot or a foot to be set down on a next step up. With a hipflexion and a low-torque lift of a prosthetic foot or of the distallyarranged orthopedic element, a knee angle can be obtained which, in theevent of the hip being brought forward or in the event of acorresponding extension by the force of gravity, is sufficient toovercome the edge of a step or to climb over an obstacle and positionthe prosthetic foot or the distally arranged orthopedic element over thestep or set it down behind the obstacle. It is advantageous for theweight to be distributed in such a way that the center of gravity isarranged as far distally as possible, such that, without an increase inthe overall weight of the orthopedic appliance, the desired effect ofthe knee flexion is reached with a low-torque lift of the prostheticfoot or of the distally arranged orthopedic element.

A low-torque lift can be detected by measurement of a horizontalacceleration of the distally arranged orthopedic element and bydetection of a bending in the joint.

In principle, provision is likewise made for flexion to be supported inthe lift phase via a pretensioned spring mechanism; in addition to aflexion of the knee, a plantar flexion of the foot can also take place,such that the front part of the foot is set down.

After the flexion damping has been reduced, a free extension can be setwith time control, such that only the system-inherent resistances areactive in the extension direction. The time control can be effectedmechanically or electrically. The parameters are preferably determinedduring walking, in order to be able to permit a change via the actuatorswithout interrupting the movement sequence.

In addition to control in the extension direction or flexion direction,provision is likewise made for control in another degree of freedom,e.g. in the medial-lateral direction, or in combined forms thereof.

Such control is expedient, for example, in hip joints or ankle joints.Other rotary or translatory degrees of freedom can also be influenced bythe control.

Illustrative embodiments of the invention are explained in more detailbelow with reference to the figures, in which:

FIGS. 1 to 6 show a schematic sequence of alternating stair-climbingwith a passive knee joint prosthesis;

FIG. 7 shows a schematic depiction of the method;

FIGS. 8 to 10 show variants of the method.

FIG. 1 shows a prosthesis wearer 1 with a knee joint prosthesis 2, whichis secured by upper attachment means to a thigh stump. The prostheticleg 20 stands with the healthy contralateral leg 4 in front of a step.

To reach the next step up, a prosthetic foot 6 has to be guided over thestep edge. An active bending of the hip, as is indicated by the arrow 7,assists the passive bending of the knee, which is shown by the arrow 8and which, because of the mass inertia both of the prosthetic foot 6 andalso of the connection element 3, is effected from the prosthetic kneejoint 2 to the prosthetic foot 6. For this purpose, a minimum flexiondamping is required to ensure that, after a flexion of the hip, theprosthetic foot 6 does not swing forward and is not moved against theriser or under the step 5. In the lift phase, as shown in FIG. 2, theaim is for the prosthetic foot 6 to be guided upward, as far as possiblein a perpendicular manner, this possibly being initiated by a slightrearward movement. The lift is detected via the flexion angle betweenthe connection element 3 and the thigh or via a reduction of the axialforce in the connection element 3, without flexion of the prostheticfoot 6. It is also possible to detect the stair-climbing mode, and thusthe lowering of the flexion damping to a value below the normal swingphase control, preferably to the minimum value, via a horizontalrearward movement of the prosthetic foot 6 in conjunction with a bendingof the hip.

After the step edge has been negotiated and the lift phase completed, asis shown in FIG. 2, a secure positioning of the prosthetic foot 6 on thestep is required. For this purpose, the prosthetic foot 6 has to bemoved forward, which can be achieved by extension as a result of theforce of gravity. For this purpose, an extension damping can be reduced,if this has not already been done in the lift phase. A prosthetic kneejoint 2 that is sufficiently damped in flexion and extension prior tostraightening allows the prosthesis wearer 1 to position the prostheticfoot 6, by means of the hip angle being changed. In the lowering andhip-straightening phase, the flexion and extension are preferablystrongly damped in order not only to control the set-down, but also toprevent spontaneous falling back in the event of the hip-straighteningtorque being insufficient. The extension remains damped so as to be ableto control the speed of straightening of the hip and knee. This is shownin FIG. 3.

In FIG. 4, the set-down phase is completed. The prosthesis wearer 1 caninitiate straightening of the knee with a hip-straightening torque. Thestraightening of the knee can be assisted by an extension of the healthyfoot.

FIG. 5 shows the increasing straightening of the knee throughapplication of a hip torque. The increasing straightening of the kneeshortens the effective lever and facilitates the straightening of theknee through the straightening of the hip.

FIG. 6 shows the complete extension of the leg provided with the kneejoint prosthesis 2. The contralateral leg 4 is moved past the prostheticleg 20 and placed on the next step up, such that alternating climbing ofstairs is possible with the passive knee joint prosthesis.

Accordingly, the control is configured in such a way that, during thelift of the prosthetic foot 6, a flexion resistance is set that permitsa knee angle α, which allows the prosthetic foot 6 to be placed on thenext step. Flexion support by spring mechanisms may facilitate thelifting movement and make it easier to negotiate the step height.

If no action is to take place after the stair-climbing mode has beentriggered by detection of a low-torque lift, a free extension is set,said free extension being set in a time-dependent manner. The timefunction can also be mechanical. The low-torque lift can be detected viathe mass inertia, if the healthy leg is first set down and only thesecond step is intended to be negotiated by the leg provided with theprosthesis. If the prosthetic foot is first unloaded and the prostheticknee joint then bent, the stair-climbing mode is to be set. The dampingboth in the direction of extension and also in the direction of flexionafter the lift phase, that is to say during the hip-straightening phase,is maintained until a complete extension of the prosthetic knee joint isreached or detected.

FIG. 7 shows a schematic depiction of the method. Proceeding from astarting position A, which is detected by sensors on the prosthesis ororthosis, the sensor data are compared with predefined values or valueranges that have been stored in a memory unit and have been combined toform various criteria K. Several signal states or signal profiles fromthe sensors preferably describe a criterion K.

If, for example, a specific axial force in connection with a knee angleor with a vertical movement is measured, corresponding values of thesensors can result in the criterion that the special function S ofovercoming an obstacle is to be set, which leads to a correspondingadjustment of the extension damping and flexion damping. Similarly, thecriterion K for the special function S of overcoming an obstacle can besatisfied when there is a rapid drop in the axial force, when the kneeis straightened or being straightened and when the axial force is belowa level, such that corresponding damper adjustments have to be made. Thedetected criteria K trigger the respectively required actions, forexample a reduction or increase in the flexion damping and/or extensiondamping, the release of a catch, the adjustment of a drive, or theadjustment or canceling of a limit stop.

The overcoming of obstacles can also be detected, for example, when anaxial force drops below a defined level and a knee is straightened,likewise a criterion can be reached by satisfying a defined inclinationof the lower leg or of a below-knee rail in space, a knee angle and alow knee torque. A vertical acceleration upward, with a straightenedknee and with a relatively low axial force level, can likewise be acriterion for a special function, for example the overcoming of anobstacle or alternating climbing of stairs.

It is further possible, proceeding from the starting position A, tocompare several signal states or profiles with various criteria K. Thecomparing of several criteria K with one another, and of several signalstates in one criterion K, provides increased safety. The greater thenumber of signal states or profiles within a criterion K, the moreprecisely it is possible to determine the respective state of theorthopedic appliance or of the patient, and the walking situation isthereby also more precisely described. On the basis of this informationand of the signal states or profiles within the parameters provided fora criterion K, it is then possible, for example, to specifically changethe damper characteristics and the movement pattern of the orthopedicappliance.

Several criteria K can trigger the same special function K, therebyproviding greater safety in respect of correct detection of a movementstate. This is necessary in view of the fact that special functions S,such as stepping over an obstacle or alternating climbing or descendingof stairs, differ significantly in terms of their movement patterns fromthose of walking on a plane, but this special function S is difficult todetect from walking on a plane. Whereas this was previously made easierby particularly pronounced movements being performed in order to set aspecial function S, for example a repeated rocking movement of the frontof the foot, the method according to the invention permits automaticadaptation of the damping behavior to the particular walking situation.

Walking on a plane normally requires shortening of the leg that is to bemoved forward after the foot is lifted. If the leg is not shortened,sufficient ground clearance can be generated by lifting of the hip orcircumduction. Physiologically, the leg is also shortened by bending ofthe knee. In leg prostheses that replace the knee and the lower leg, theweight relationships of the lower leg, and the time and motor factorsinvolved in walking, have the effect that the lower leg swings too farrearward and, consequently, the leg prosthesis is not straightened intime and cannot therefore be loaded. Patients therefore walk veryslowly, or the prostheses are equipped with a suitable swing phasecontrol that significantly damps the swing behavior of the lower leg.High-performance flexion damper systems take account of differentwalking speeds and always provide enough freedom of the leg to ensurethat the prosthesis users do not stumble, but the leg is straightenedagain in time for the following loading phase. The more quickly the userwalks, the more the damping takes effect.

To climb stairs, a knee has to be bent much more than when walking on aplane, so as to avoid the leg being left suspended in front of the edgeof the step that is to be negotiated. The reduced flexion damping canalso be exploited in order to overcome small obstacles in one step.However, for the reasons mentioned above, the low flexion dampingnecessary for this purpose is not suitable for walking on a plane. Fordetection of the respectively required flexion damping for the step thatis to be taken, a plurality of sensor data can be combined within onecriterion and can trigger a special function when correspondingparameters are satisfied. If the tilting of the lower leg in space isevaluated, a low flexion resistance for climbing stairs can be activatedwhen the prosthesis or orthosis is unloaded and the knee is not bent. Ifthe prosthesis leg is unloaded with the knee straightened, a low flexionresistance for climbing stairs can be activated by the speed of thereduction in load even before the prosthesis is completely unloaded. Theuser in this way has more time to initiate bending. In order to ensurethat flexion damping is not deactivated too early, for example when adrop in axial force is detected while standing in a vehicle travelingover bumpy ground, the absolute value of the axial force can be used asadditional parameter for a criterion.

It is likewise possible, by evaluating the angle profiles of the thighand lower leg, to distinguish between climbing stairs and walking on aplane. If the thigh is bent slightly rearward, a reduction of theflexion damping can be expected.

For control of an ankle joint, it is advantageous to determine when thetoe area or the front of the foot is move rearward in order to overcomea step or an obstacle. No dorsal flexion should be allowed when the heelis set down, so as to make climbing stairs easier.

Accordingly, the resistance to a dorsal flexion is increased afterset-down. By contrast, when going down a set of stairs, a strong plantarflexion is desirable at set-down. In order to permit complete set-downof the prosthetic foot or of the foot holder, a dorsal flexion should bepermitted, but this should be done increasingly with a resistance inorder to ensure controlled set-down.

In principle, a resistance to straightening is also necessary in thejoint appliance, particularly in the knee joint, in order to teach apatient active control and action. Orthopedic knee joints that permitwalking down a set of stairs are known from the prior art. By means of ahigh degree of damping in the flexion direction, the user of theorthopedic appliance can bend the knee joint in a controlled manner andthus reach the next step. The high degree of flexion damping results ina uniform movement and thus relieves the load on the contralateral side.When climbing stairs, the movement in a healthy knee joint is supportedby a knee-straightening torque. This torque is provided by muscles.Orthopedic appliances are known that comprise a knee joint which permitsstraightening of the knee by means of actuators. Because of the energyrequired and the forces that occur, a relatively heavy knee joint isneeded that is dependent on external energy.

In the case of orthoses or prostheses of the lower extremity, it is inmany cases possible to generate a sufficiently high straightening torquefrom the hip in order to straighten the knee when climbing stairs.However, as soon as the knee begins to straighten, it moves rearward,relative to the center of gravity of the body, such that theknee-straightening torque increases. This effect is self-intensifying.The increasing effective lever arm results in uncontrolledstraightening, with a hard, uncomfortable end stop. In order to adaptthe orthopedic appliance to climbing stairs without external energybeing supplied, provision is made for the control to significantlyincrease the extension damping via an adjustable actuator after set-downon the next step up. This damping acts counter to the straighteningtorques acting on the knee joint and is preferably chosen so as topermit an almost constant and easily controllable straightening. Thiscan be ensured simply by constant damping. It is likewise possible toprovide damping that increases with straightening, in order tocompensate for the effect whereby, with increasing straightening of theknee joint relative to the center of gravity of the body, the knee jointis exposed to a greater effective lever arm.

The set-down on the next step up, with a bent knee joint, can optionallybe performed via sensors arranged on the orthopedic appliance or via anactuator that can be activated mechanically upon set-down, for example apiston that is displaceable in the joint as a result of the axial forceon the orthopedic appliance. The extension damping is in this caseincreased to a level that markedly exceeds the level for walking on aplane.

FIG. 8 shows a variant of the invention in which, proceeding from astarting position A1, a special function S1 can be called up via severalcriteria K. If several parameters are determined on the orthopedicappliance, different parameters can be combined to foam differentcriteria. It is thus possible for two different criteria to lead to theinitiation of a special function S.

FIG. 9 shows a variant of the invention in which, proceeding fromdifferent starting positions A1, A2, exactly one special function S1 canbe called up via different criteria K.

FIG. 10 finally shows that it is possible, from one starting positionA1, to switch to various special functions S1, S2, S3 via variouscriteria K and parameter profiles. It can thus happen that identicalinstantaneous values of the respective parameters are present in thestarting situation A1, for example axial force, knee angle and torque,but different walking situations can be predicted from the profiles ofthese parameters and, as a result, corresponding special functions S1,S2, S3 can be initiated, by means of drives being switched on or off,energy stores being released, damper devices varied or brakes activated.Similarly, limit stops can be adjusted and catches released.

1-26. (canceled)
 27. A method for controlling a passive prosthetic kneejoint, the method comprising: providing a prosthesis having the passiveprosthetic knee joint, an upper attachment member configured to attachto a limb, a lower attachment member pivotally attached to the upperattachment member, an actuator, a computer unit, and a plurality ofsensors; detecting parameters of the prosthesis with the plurality ofsensors, the parameters including at least an absolute angle of thelower attachment member relative to a vertical axis, a rate of change ofthe absolute angle, a torque force in the knee joint, and a rate ofchange of the torque force; comparing the detected parameters withcriteria stored in the computer unit; selecting multiple criterion basedon the comparing; automatically adjusting, with the actuator, at leastone of a damping force or a damping profile for the knee joint inaccordance with the selected criterion, to adapt to special functionsthat deviate from walking on a planar surface.
 28. The method as claimedin claim 27, wherein the parameters further include at least one of ajoint angle and a profile of a change in the joint angle.
 29. The methodas claimed in claim 27, wherein the parameters further include at leastone of an axial force and a profile of the axial force.
 30. The methodas claimed in claim 27, wherein the parameters further include at leastone a vertical movement and a profile of a vertical movement.
 31. Themethod as claimed in claim 27, wherein the parameters further include atleast one of a horizontal movement and a profile of a horizontalmovement.
 32. The method as claimed in claim 27, wherein the parametersfurther include at least one of a tilt angle of part of the prosthesisin space and a profile of a change in the tilt angle of part.
 33. Themethod as claimed in claim 27, wherein at least two parameters orparameter profiles are combined in one criterion.
 34. The method asclaimed in claim 27, wherein multiple criteria are used to initiate oneor more of the special functions.
 35. The method as claimed in claim 27,wherein in at least one of the special functions, the damping isautomatically changed in a set-down phase or a hip straightening phase.36. The method as claimed in claim 27, wherein at least one of thespecial functions is initiated when an axial force acting on a lower legdrops and when the passive prosthetic knee joint is straightened orbeing straightened.
 37. The method as claimed in claim 36, wherein theat least one of the special functions additionally takes into account anaxial force dropping below a fixed level.
 38. The method as claimed inclaim 28, wherein at least one of the special functions is initiatedwhen a lower leg is inclined rearward, the passive prosthetic knee jointis straightened, and a knee torque is below a fixed level.
 39. Themethod as claimed in claim 27, wherein the parameters further include atleast one a vertical acceleration and an axial force, and the specialfunction is initiated when there is an upward vertical acceleration andwhen an axial force is below a fixed level.
 40. The method as claimed inclaim 27, wherein the parameters further include at least one a verticalacceleration and an axial force, and the special function is initiatedwhen there is a rearward horizontal acceleration and when an axial forceis below a fixed level.
 41. The method as claimed in claim 27, whereinthe damping is adjusted during at least one of a lift phase and theset-down phase.
 42. The method as claimed in claim 27, wherein thedamping is adjusted during a stance phase or during a swing phase. 43.The method as claimed in claim 27, wherein a low-torque lift of thedistally arranged lower attachment member is detected via a force sensoror torque sensor.
 44. The method as claimed in claim 27, wherein theparameters further include at least one a vertical acceleration of thedistally arranged lower attachment member and a joint angle, and alow-torque lift is detected by measurement of the vertical accelerationand by detection of a bending in the passive prosthetic knee joint. 45.The method as claimed in claim 27, wherein after the automaticadjustment of the damping force or damping profile, setting a freeextension with time control.
 46. The method as claimed in claim 45,wherein the time control is effected mechanically or electronically. 47.The method as claimed in claim 27, wherein the parameters are determinedduring walking.
 48. A method for controlling a passive prosthetic kneejoint, the method comprising: providing a prosthesis having the passiveprosthetic knee joint, an upper attachment member configured to attachto a limb, a lower attachment member pivotally attached to the upperattachment member, an actuator, a computer unit, and a plurality ofsensors; detecting parameters of the prosthesis with the plurality ofsensors, the parameters including at least an axial force in the lowerattachment member, a torque force in the knee joint, and a rate ofchange of the torque force; comparing the detected parameters withcriteria stored in the computer unit; selecting multiple criterion basedon the comparing; automatically adjusting, with the actuator, at leastone of a damping force or a damping profile for the knee joint inaccordance with the selected criterion, to adapt to special functionsthat deviate from walking on a planar surface.
 49. The method as claimedin claim 48, wherein the parameters further include at least one of ajoint angle and a profile of a change in the joint angle.
 50. A methodfor controlling a passive prosthetic knee joint, the method comprising:providing a prosthesis having the passive prosthetic knee joint, anupper attachment member configured to attach to a limb, a lowerattachment member pivotally attached to the upper attachment member, anactuator, a computer unit, and a plurality of sensors; detectingparameters of the prosthesis with the plurality of sensors, theparameters including at least a joint angle of the knee joint, anabsolute angle of the lower attachment member relative to a verticalaxis, and a torque force in the knee joint; comparing the detectedparameters with criteria stored in the computer unit; selecting multiplecriterion based on the comparing; automatically adjusting, with theactuator, at least one of a damping force or a damping profile for theknee joint in accordance with the selected criterion, to adapt tospecial functions that deviate from walking on a planar surface.
 51. Amethod for controlling a passive prosthetic knee joint, the methodcomprising: providing a prosthesis having the passive prosthetic kneejoint, an upper attachment member configured to attach to a limb, alower attachment member pivotally attached to the upper attachmentmember, an actuator, a computer unit, and a plurality of sensors;detecting parameters of the prosthesis with the plurality of sensors,the parameters including at least an axial force in the lower attachmentmember, a joint angle of the knee joint, and a torque force in the kneejoint; comparing the detected parameters with criteria stored in thecomputer unit; selecting multiple criterion based on the comparing;automatically adjusting, with the actuator, at least one of a dampingforce or a damping profile for the knee joint in accordance with theselected criterion, to adapt to special functions that deviate fromwalking on a planar surface.
 52. A method for controlling a passiveprosthetic knee joint, the method comprising: providing a prosthesishaving the passive prosthetic knee joint, an upper attachment memberconfigured to attach to a limb, a lower attachment member pivotallyattached to the upper attachment member, an actuator, a computer unit,and a plurality of sensors; detecting parameters of the prosthesis withthe plurality of sensors, the parameters including at least an axialforce in the lower attachment member, a rate of change of the axialforce, and a joint angle of the knee joint; comparing the detectedparameters with criteria stored in the computer unit; selecting multiplecriterion based on the comparing; automatically adjusting, with theactuator, at least one of a damping force or a damping profile for theknee joint in accordance with the selected criterion, to adapt tospecial functions that deviate from walking on a planar surface.